Despite the extensive work being performed to understand cancer and carcinogenic properties of chemicals and other agents, there are still gaps in our ability to efficiently identify carcinogens, and elucidate their mode(s) of action. The current state of assays designed to examine mutation and carcinogenic mechanisms are especially limited by their high costs and low throughput capacities. This laboratory has developed a gene mutation assay that is based on the endogenous Pig-a gene. The Pig-a gene product is essential for the biosynthesis of glycosyl phosphatidylinositol (GPI) anchors. Mutations giving rise to nonfunctional GPI anchors prevent certain proteins from being expressed on the cell surface, and this represents a phenotype that can be measured by flow cytometry. The work proposed herein will extend our development efforts by creating a suite of assays that represent a platform for studying a key mode of carcinogenic action, mutation. By devising Pig-a based methods that examine cells in culture, laboratory rodents, and human subjects, a truly comprehensive bridging biomarker will be realized. The bridging capabilities and high throughput nature of the proposed mutation assessment tools will contribute significantly to important areas of research that include academic, regulatory, and industrial settings.